Battery-driven personal computers support a popup menu function.
Any item the user of a personal computer has set or changed in the popup menu is stored as a computer-system configuration in a battery backed-up CMOS RAM, even if the user does not turn off the power switch or perform resetting (reboot). In other words, menu items can be changed without turning off the power switch or performing reboot (re-reboot).
The popup menu function achieves, for example, the gradation control for the built-in display, the ON/OFF setting of the battery and the system speaker, the power ON/OFF control of the built-in modem, and the setting of the AUTO OFF time for the HDD (Hard Disk Drive).
The popup menu is activated when a specified key on the keyboard is depressed and is displayed on the display.
Most of battery-driven personal computers support a VGA (Video Graphics Array) which is a display-controlling means. The VGA includes palette registers for storing color-designating data.
The VGA comprises an EGA (Enhanced Graphics Adapter), color registers, and D/A converters for performing D/A conversion on the values held in the color registers.
The 400-line scheme is standard for the VGA, whereas the 350-line scheme is standard for the EGA. The VGA can provide high resolution of 640.times.480. This makes analog display possible, in which 256 colors can be selected from 262144 colors, instead of selecting 16 colors from 64 colors in the EGA.
Hitherto, only the data in the VRAM is rewritten before displaying the popup menu on the display screen. This measure is taken in order not to change the condition (color) in which to display the popup menu on the display screen.
In some applications, the values set for the palette registers and the color registers, both used to display characters of the popup menu, are identical to the values set for the palette registers and the color registers, both used to display screen background (screen-background color). If this is the case, the popup menu characters and the screen background will be displayed in the same color. Consequently, the popup menu will not be seen on the screen.